One-piece plurifocal lens



Dec. '2, 1943.

W. R. UHLEMANN 2,336,322 ONE-PIECE PLURIFOCAL LENS 2 Sheets-Sheet 1 Filed Feb. 23, 1940 w I \wmm 1943- w. R.'UHLEMANN 2,336,322

ONE-PIECE PLURIFOCAL LEN:

1 Filed Feb 23, 1940 2 sheets-sheet 2 r r I Patented Dec. 7, 1943 ONE-PIECE PLURIFOCAL LENS William R. Uhlemann, Evanston, Ill., assignor to Uhlemann Optical 00. of Illinois, Chicago, 111., a corporation of Delaware Application February 23, 1940, Serial No. 320,403

3 Claims.

My invention relates to one-piece plurifocal lenses.

One of the objects of my invention is to provide an improved method of making a onepiece plurifocal lens. Another object is to provide an improved lens blank for use in making a one-piece plurifocal lens. Another object is to provide an improved method which enables lens blanks to be furnished to opticians with a readin field cavity coextensive with the reading field already ground therein to a base curvature, whereby the optician, by keeping on hand a relatively small stock of these partially ground blanks of a few assorted base curves, may by simple grinding processes complete the lens to accommodate many different kinds of prescriptions, including prescriptions calling for different degrees of prismatic angularity and those calling for so-called cylindrical as well as for spherical surfaces for certain vision fields.

Further objects and advantages of the invention will be apparent from the description and claims.

In the drawings, in which my invention is exemplified,

Figure 1 is a sectional view of a lens blank which may be used in forming a one-piece plurifocal lens;

Fig. 2 is a sectional view showing the lens blank with the posterior surface of the reading field ground therein;

Fig. 3 is a sectional view showing the lens blank and tool with the posterior surfaces of the reading field and distance field ground thereon;

Fig. 4 is a sectional view of the lens and tool showing the lens completed with the anterior surface of the distance field and reading field ground thereon;

Fig. 5 is a fragmentary view of the lens showing one configuration of the reading field;

Fig. 6 is a sectional view showing a lens blank and tool with the anterior surface of the reading field ground therein;

Fig. '7 is a sectional view showing the lens and tool with the posterior surfaces of the reading and distance fields ground thereon; and

Fig. 8 is a transverse sectional view showing the completed lens and the grinding tool with the anterior surface of the distance field ground thereon.

In general, the method involves making a onepiece plurifocal lens I from a lens blank 2, which method comprises grinding a depression 3 in one of the faces of the lens, either the anterior surface or the posterior surface, this depression being coextensive with the reading field and having a spherical surface which may be considered the basic lens surface, thereafter grinding the face of the blank in which the depression 3 is formed to an extent to cover the distance field 4 only, and grinding the opposite face of the blank to an extent to cover both the reading field and the distance field and of a curvature to give the desired total refraction both to the reading field and to the distance field.

Before describing in further detail the method, I will describe briefly the apparatus used in forme ing the various lens surfaces. Referring, first, to Figs. 1 to 5, inclusive, the tool 5 used in forming the depression 3 in the lens blank 2 may be substantially like that disclosed in my prior Patent No. 1,881,982, dated October 11, 1932, comprising a cylindrical grinding tool having a circular annular cutting edge which is rotated about an axis 6 which extends through the cen-, ter of the circle of the cutting edge 1 and is perpendicular to the plane of said circle, the cutter at the same time being swung about a fixed center, which center is on the same side of the lens as the tool so that the axis 6 oscil lates with respect to the lens asthe tool 5 rotates about the axis 6, whereby an elongated cavity is formed, the bottom surface of which is spherical and forms the envelope of the various positions of said annular cutting edge. In using this tool, the grinding or cutting is effected solely by the outer edge of the bottom portion of the grinding or cutting tool, the rest of the bottom portion of the cutting tool being spaced from the bottom of the cavity due to the swinging action of the cutting tool and due to the shape of the bottom portion of the cutting tool.

The shape of the bottom portion of the cutting tool may be either fiat as shown in Fig. 2 where a concave surface is to be formed, or concave as shown at 8 in Fig. 6 where a convex surface is to be formed on the lens. However, the tool must be so formed that no part of the bottom portion of the tool is farther from the axis about which the cutting tool swings than are the points in the circular edge of the bottom of the cutting tool.

After grinding the posterior surface of the reading field, as in Fig. 2, and before performing the grinding operation as shown in Fig. 3 for the posterior surface of the distance field, the reading field cavity may be covered or masked with a very thin coat or film Illa of some suitable easily protective material to prevent any harmful effects on the reading field due to the action of grinding the distance field.

For performing the operation shown in Fig. 3, in which the posterior surface of the distance field is ground, the tool may be either a tool for forming a concave spherical surface, in which case a simple grinding tool 9a having a convex spherical surface If! and rotatable about a fixed axis may be used, or, if a so-called cylindrical surface is desired, a tool may be used having the desired surface conformation and having a compound movement with respect to the lens to be ground.

For performing the operation shown in Fig. 4, in which the anterior surfaces, both of the reading field and distance field, are ground, the tool may be either a tool for forming a convex spherical surface, in which case a simple grinding tool 9 having a concave spherical surface If; and rotatable about a fixed axis may be used. or, if a so-called cylindrical surface is desired, a tool may be used having the desired surface conformation and having a compound movement with respect to the lens to be ground.

If some degree of prism is desired in the reading field, this may be obtained by the workman by calipering the edges of the lens when performing the operations shown in Figs. 3 and 4. By now and then calipering the edges to determine the thickness of the opposite edges of the lenses in the operation shown in Fig. 3, the operator can determine the lengths a and b. and by means of suitable charts can so grind the lens that the desired degree of prismatic effect will be obtained in the reading field outlined by the depression 3.

In Fig. 4, by calipering the edges occasionally. the operator can o grind the lens that the distances 0 and at will be equal, thus getting rid of the prismatic effect in the distance fiield while retaining the prismatic effect in the reading field.

The apparatus and operations disclosed in Figs. 6, 7 and 8 are quite similar to those described in connection with 1, 2, 3 and 4, except that in Figs. 6, 7 and 8 the master lens surface is ground on the convex anterior side of the lens. Let it be assumed by way of illustrating a different sequence of operation from that described with reference to Figs. 1 to 4, inclusive, that the operation shown in Fig. '7 is performed before the operation shown in Fig. 8. In this apparatus and operation, the tool 5 for grinding the master curve cavity on the anterior side of the blank must have its end somewhat concave as indicated at 8 in order to make sure that the grinding is done entirely by the edge of the tool and the tool in the swinging movement of the axis 6 must swing about a center below the lens or, in other words, on the side of the lens opposite to that on which the tool lies.

In grinding the lens, a blank is first formed as shown in 6 to provide the master curve cavity, with a convex spherical surface to form the basic lens surface. Thereafter, the posterior surface, both on the reading field and the distance field, may be ground on a convex tool I I to give the desired curvature both to the posterior surface of the reading field and to the posterior surface of the distance field.

For grinding the anterior surface of the distance field, a tool Ila as shown in Fig. 8 may be used, having a concave surface which may have either a spherical surface or a so-called cylindrical surface. Here, also, by occasionally calipering the edges of the lens and by bearing harder on one edge of the lens than on the other, the distances a, b, c, and d may be made to give the desired angle of prism to the reading field and to get rid of the prismatic effect in the distance field. Any desired degree of prismatic effect may be given to the reading field by using the methods described in connection with Figs. 3 and 4.

In explaining how the Optician, having a stock of blanks with master curve cavities coextensive with the reading field ground thereon, may grind a lens according to a definite prescription, the following symbols are used in the specification and drawings:

A=focal length of composite distance field expressed in diopters l3=focal length of posterior surface of distance field expressed in diopters C=focal length of anterior surface of distance field expressed in diopters D=focal length of complete reading field expressed in diopters E=focal length of posterior surface of reading field expressed in diopters F=focal length of anterior surface of reading field expressed in diopters From the laws of optics the following equations are true:

Assume that a prescription calls for the following:

A=+2.00 D=A+2.50=+4.50

The problem for the optician is to choose a blank having a suitable master surface for the reading segment already ground therein and to find B and C in order to enable him to grind the remaining surfaces properly to comply with the prescription. The optician may choose for this prescription either a lens blank having ground therein a concave master surface for the reading segment on the posterior face of the blank having a focal length E, as in Figs. 1 to 4, inclusive, or he may choose a lens blank having a convex master surface for the reading segment ground therein on the anterior face of the lens having a focal length F as in Figs. 6, 7 and 3.

Let it be assumed, for one example, that the optician chooses a lens blank having a concave master surface ground on its posterior face, having a focal length expressed in diopters of 3.00 or in other words E=3.00. From Equation 2 above, D=E+F. Substituting values for D and E in Equation 2, gives +4.50=3.00+F, from whence it is determined that F=+7.50.

When, as in the case assumed, a blank is chosen having ground therein a concave master surface for the reading segment on its posterior face, as in Figs. 1, 2, 3 and 4, the focal length C of the anterior surface of the distance field will be the same as the focal distance F of the anterior surface of the reading field, as they are both ground on a common grinding tool. In this case then C=F=+ 7.50.

The Equation 1 above reads A=B+C. Substituting values for A and B gives +2.00=1.50+C, whence C'=+3.50. That these values of B and C will satisfy the above prescription for A and B is apparent from a substitution of values in Equations 1 and :2 as follows: From Equation 1 A=B+C. From Equation 2 D=E+F. Substituting values for B and C in Equation 1 The prescription in question, as indicated above, reads: A=+2.00 D=A+2.50

from whence we find that From Equation 2 above, D=E+F. Substituting values in Equation 2 gives 4.50=E+6.00. From this it is determined that E=-1.50.

When, as in this case, a blank is chosen having ground therein a convex master surface for the reading segment in its anterior surface, as in Figs. 6, 7 and 8, the focal length B of the posterior surface of the distance field will be the same as the focal length E of the posterior surface of the reading field, as these surfaces are both ground on a common grinding tool. In this case then B=E. Substituting value for E gives B=-1.50.

In Equation 1 A=B+C. Substituting values for A and B gives +2.00=-1.50+C. From this equation we find that C'=+3.50.

That the above derived Values for B and C satisfy the prescription in question is proven as follows:

Equation 2 reads D=E+F. Substituting values for E and F, we find that D=-l.50+6.00=+4.50. It will be seen that this value for D satisfies the prescription.

Equation 1 reads as follows:

A=B+C. Substituting values for B and C gives the equation A=-1.50+3.50. From this it appears that A=+2.00 which satisfies the prescription in question.

If the prescription calls for a prism effect in the reading field, for example, for two degrees of prism, this may be obtained by the optician in his grinding operations by calipering the edges of the lens at a, b, c, and d. Let it be assumed by way of illustrating a different sequence of operation from that described with reference to Figs. 1 to 4, inclusive, that the operation shown in Fig. 7 is performed before the operation shown in Fig. 8. In that grinding operation shown in Fig. I, which covers both the distance field and the reading field, the optician can so grind this surface as to give the proper caliper measurements at a and b to give the desired prism efiect to the total reading field. In the grinding operation shown in Fig. 8, which covers the distance field alone, by calipering the edges of the lenses at c and d in the grinding operation, the optician can so grind the surface as to make the distance equal to the distance cl, which will result in the distance field having no prismatic effect while leaving the prismatic effect desired in the reading field.

From the preceding description of Figs. 1 to 4, inclusive, and Figs. 6, '7 and 8 it is obvious that, by taking the proper precautions, it will be possible for the optician to grind the posterior face of the lens before grinding'the anterior face, or vice versa.

It is intended that the local optician carry rough blanks with the base curves of reading segments ground into the rough blank as master curves of reading segments only and that these blanks be finished by the optician to make a lens of almost any desired prescription, including either a sphere or cylinder with a prism of any strength desired simply by surface grinding. This aids materially in reducing the expense of making bifocals or trifocals.

These plurifocal lenses are made from a glass of single index of refraction and depend entirely upon pure and true optical curves for their foci and not upon density of media as is always the case with a fused bifocallens.

In carrying out the method, the workman at the central distributing station takes a rough pressed blank of meniscus shape and grinds off the rough surfac on either side. The reading segments can be put on either the convex or concave surfaces and at present in the process both surfaces are left unpolished. After the rough surface has been removed, which makes it easier to grind the segment on a specially constructed machine, the workman selects the tool for grinding the segment of any desired diameter. He mounts the lens on a specially constructed block built to fit the machine and then the lens is cemented by means of any proper adhesive materia1 such as pitch, etc. The block is held firmly in the proper device and four graduated pins are pressed against the heated lens and pitch so that the lens is forced to assume a position such that no prismatic effect is ground on the lens while th reading segment is being ground.

If the reading segment is ground without a prismatic effect and is perfectly symmetrical as to depth of segment, the local optician, who gets a stock of blanks from the central distributing station, is able to produce any prismatic effect desired in the segment by grinding the distance portion of the lens in the form of a prism on either the anterior surface or posterior surface.

This form of lens is especially effective in what is known to the industry as cataract lenses for persons who have had th crystallin lens of the eye removed, its function being replaced by a lens placed in front of the eye.

Such lenses made for cataract eyes can be made to resemble closely in function the crystalline lens of the eye since this type of lens can be made in the biconvex form.

The cataract bifocal lens of this type can be made much thinner than the ordinary typ of cataract lenses.

It is a particular advantag of the present invention that the diificult and exacting work of properly grinding recessed reading areas in ophthalmic lenses of the one-piece type having recessed reading fields and th results of the expensive and complicated equipment required for this work are made instantly available to outlying opticians for the prompt filling of their ophthalmic prescriptions. The equipment necessary to manufacture plurifocal lenses of this type has been heretofore a serious limitation to their use.

It will be noted that the present method of grinding ophthalmic lenses permits th production of any degree of prismatic angularity in the reading field by action other than upon the recessed reading field of the lens.

Another advantage of the practice of the present invention is that if corners adjacent'the recessed reading field break so as to form irregularities these irregularities may be removed by the subsequent grinding operation covering the distance field.

At the same time that the reading field pree scription is, in effect, modified, the distance field surfaces are also ground and polished, whereby, with a minimum of time and effort, a satisfac tory plurifocal lens is produced.

Further modifications will be apparent to those skilled in the art and it is desired, therefore, that the invention be limited only by the scope of the appended claims.

Having thus described my invention, What I claim and desire to secure by Letters Patent is:

1. A method of making a one-piece plurifocal lens from a lens blank, which method comprises at least three grinding operations including (1) grinding a depression having a spherical surface on one face of the lens blank coextensive with the reading field, said depression having its peripheral walls ground normal to said spherical surface, said depression being ground deep enough to enable the vision field surrounding the depression to be ground to form any one of a number of surfaces having substantially different centers of curvatures and thereafter (2) grinding the opposite face of the lens blank to an extent to include the reading field and another vision field and of a curvature to give the desired total refraction to the reading field and (3) grinding the face of the blank on which said spherical surface is formed to an extent to include said other vision field and to exclude th reading field and of a curvature to give the desired total refraction to said other field, the sequential order of operations (2) and (3) being optional.

2. A method of making a one-piece plurifocal lens from a lens blank, which method comprises at least three grinding operations'including (l) forming a depression having a spherical surface on one face of the lens blank coextensive with the reading field, said depression having its peripheral walls ground normal to said spherical surface, said depression being ground deep enough to enable the Vision field surrounding the depression to be ground to form any one of a fixed center, and said a number of surfaces having substantially different centers of curvature and thereafter (2) grinding the opposite face of the lens blank to an extent to include the reading field and another vision field and of a curvature to give the desired total refraction to the reading field and (3) grinding the face of the blank on which said spherical surface is formed to an extent to include said other vision field and to exclude the reading field and of a curvature to give the desired total refraction to said other field, the sequential order of operations (2) and (3) being optional, said depressed spherical surface being the envelope of the circular edge of the end of a right circular cylinder, th axis of which is shifted about a fixed center, and said peripheral walls being the envelope of the circumferential surface of said cylinder.

3. A method of making a one-piece plurifocal lens from a lens blank, which method comprises at least three grinding operations including (1) forming a depression having a spherical surface on one face of the lens blank coextensive With the the reading field, said depression having its peripheral walls ground normal to said spherical surface, said depression being ground deep enough to enable the Vision field surrounding the depression to be ground to form any one of a number of surfaces having substantially different centers of curvature and thereafter (2) grinding the opposite face of the lens blank to an extent to include the reading field and another vision field and of a curvature to give the desired total refraction to the reading field and (3) grinding the face of the blank on which said spherical surface is formed to an extent to include said other vision field and to exclude the reading field and of a curvature to give the desired total refraction to said other field, the sequential order of operations (2) and (3) being optional, said depressed spherical surface being of noncircular outline and forming the envelope of the circular edge of the end of a right circular cylinder, the axis of which is shifted about peripheral wall being the envelope of the circumferential surface of said cylinder.

WILLIAM R. UHLEMANN. 

